Thermal relay



1958 E. E. SIVACEK 2,846,543

THERMAL RELAY Filed Aug. 20, 1956 I INVENTOR.

[7772/ J \S'zi/dc'efz United States Patent THERMAL RELAY Emil E. Sivacelr, Ann Arbor, Mich., assignor to King- Seeley Corporation, Ann Arbor, Mich., a corporation of Michigan Application August 20, 1956, Serial No. 604,918

12 Claims. (Cl. 200-113) to move the contacts into a preselected relationship. A: wire, secured between the spring arm and an anchor, acts" in tension, when at a normal temperature, to retain movement of the spring arm, opposing the internal force of the spring. The wire, which has a finite resistance and a substantial coefficient of thermal expansion, is connected as an element of an input signalling circuit. Current through the wire produces thermal-current heating or self-heating of the wire which in turn produces a physical elongation of the wire. When the magnitude of the current is adequate, the wire will elongate sufficiently to permit the contact arm to move to its operated position, making or breaking the output-circuit controlling electrical contacts.

In general, as the magnitude of the controlled current increases, the magnitude of the electrical contact pressure must increase if the voltage drop across the contacts and the heating of those contacts is not to become excessive. However, the magnitude of the contact-closing force which can be exerted by or through the contact spring arm cannot exceed the restraining force which the wire is capable of exerting. Yet, the material and size of the wire is determined not only by these tensile strength and force-transmitting requirements, but also, and importantly, by the electrical resistance and thermal expansion characteristics of that wire.

In accordance with the principles of the present invention, a wire of appropriate electrical and thermal characteristics, but of limited diameter and tensile strength, is utilized in a force-multiplying mechanical system to permit the development of" forces adequate for the control of heavy-current electrical contacts. Means are additionally provided, representatively as an element of the aforesaid mechanical system, for enabling the magnitude of those forces to be readily adjusted.

Objects of this invention are to increase the current carrying capabilities of hot-wire type relays and to facilitate adjustment of relays of that type.

The manner of accomplishing the foregoing objects, and other objects and features of the invention, will become apparent from the following detailed description of an embodiment of the invention when read with reference to the accompanying drawings in which:

Fig. l is a plan view of a hot-wire relay embodying the principles of the present invention;

Fig. 2 is a sectional view taken substantially along the line 2-2 of Fig. 1; and

hot-

Fig. 3 is a sectional view taken substantially along .in the saddle defined by the offset portion 30.

2,846,543 Patented Aug. 5, 1958 2 electrical currents, and a suitable use for a relay of that nature is presented in the patent application of George B. Whinery, Serial No. 604,867, entitled Thermo-Responsive System, and filed on even date herewith.

The relay elements are mounted upon a support plate 10 of suitable insulating material. A bracket 12, provided with an upstanding leg portion 14 is riveted or otherwise secured to plate'10. An adjusting screw 16, carrying passive contact 18, threadedly engages a tapped aperture in leg 14, the adjusted position of contact 18 being maintained by lock nut 20.

One end of a flexible spring member 22 is attached to the upstanding leg portion 24 of another bracket 26 similarly secured to support plate 10, and the other end of that spring supports and carries the active or movable electrical contact 28. Electrical connections are made to brackets 12 and 26, or terminals electrically integral therewith, to establish the output, load or controlled circuit of the relay.

Medially of its length, spring 22 is provided with a semi-circular cylindrical offset portion 30 and with a longitudinal slot 32 extending through the offset portion 30 and a distance on either side of that portion. A bearing element in the form of a dual pulley or roller 34 having an integrally formed shaft 36 is supported by spring 22, portions of the roller 34 extending through the slot 32 in the spring 22, and the shaft 36 being seated Since the shaft 36 is longer than the width of the slot 32, the roller assembly cannot pass through the slot. Stitfening flanges 38 and 40 are provided at the upper and lower edges of the spring 22 and extend over the forward portion of the length of that spring.

The two ends of the hot wire 42 are welded or otherwise secured to the upstanding leg portions of brackets 44 and 46. Brackets 44 and 46 are riveted or otherwise secured to plate 10 and constitute, or are electrically integral with, the input terminals of the relay.

While the resistance wire 42 may simply be looped around the pulley 34, additional structure is desirably provided for not only permitting adjustment of the tension on the wire 42 but also for providing a substantial increase in the feasible force of engagement between contacts 18 and 28. Thus, a bearing element in the form of a manually adjustable cam 48 is supported by a shaft 50 upon the support plate 10. In the illustrated arrangement, cam 48 is non-rotatively mounted on shaft 50 (and may be formed integrally therewith). Shaft 50 is provided with a headed portion 52 engaging a washer 54 abutting the undersurface of plate 10, the body of the shaft passing through an aperture in that plate. A spring washer 56 is compressed between the upper face of plate 10 and the lower surface of cam 48 so that the shaft and cam may be forcefully rotated for purposes of adjustment but will not lose that adjustment in use.

In the disclosed arrangement, the hot wire 42 extends from mounting bracket 44, passes around roller 34, seating in one of the grooves therein, extends around the cam 48, seating in a circumferential groove therein, extends back to the roller 34, seating in the second groove in that roller, and then extends and is secured to the bracket 46.

Contact spring 22 is prestressed to move contact 28 into forceful engagement with contact 18. With no current passing through wire 42, the length of that wire is selected and the cam 48 is positioned so that spring 22 is deflected to move contact 28 away from contact 18, with the wire 42 being under a preselected tension. The position of contact 18 is then adjusted to establish'the appropriate contact gap. Upon the energization of the input circuit, the resultant current flow through wire 42 will produce self-heating and consequent expansion of surface, producing an immediate separation of contacts 18 and 28, terminating energization of the load.

It will be appreciated thatby virtue of the double looping permitted by the provision of cam 48, the prestressing force exerted by spring 22 may be effectively doubled over that whiclYwould 'be permissible if a resistance wire having the same tensile strength were to pass in but a single group around roller 34.

While it will be apparent that the embodiment of the invention herein disclosed is well calculated to fulfill the objects of the invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

"'1. A relay mechanism responsive to current flow in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and second mateable electrical contacts connectable in the output circuit, means securing said second contact on said base, means supporting said first contact and tending to force said first contact into a preselected relationship with said second contact, a first bearing element on said supporting means, a second bearing element supported upon said base, a wire connectable in the input circuit and adapted to elongate in response to current therethrough, and two anchor means spaced from both of said bearing elements for fixing the ends of said wire relative to said base, one end of said wire being fixed to one of said anchor means, the other end of said wire being fixed to the other one of said anchor means, said wire extending from one of said anchor means, into engagement with first bearing element, into engagement with second bearing element, and then back into engagement with said first bearing element.

2. A relay mechanism responsive to current flow in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and second mateable electrical contacts connectable in the output circuit, means securing said second contact on said base, means supporting said first contact and tending to force said first contact into a preselected relationship with said second contact, a first bearing element .on said supporting means, a second bearing-element supported upon said base, a wire connectable in the input circuit and adapted to elongate in response to current therethrough, and two anchor means spaced from both of said bearing elements for fixing the ends of said wire relative to said base, one end of said wire being fixed to one of said anchor means, the other end of said wire being fixed to the other one of said anchor means, said wire extending from one of said anchor means, into engagement with said first bearing element, into engagement with said second bearing element, and then back into engagement with said first bearing element, said second bearing element being eccentrically mounted on.

said base and rotatable to adjust the tension in said wire.

3.A relay mechanism responsive to current flow in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and second mateable electrical contacts connectable in the output circuit, means securing said second contact on said base, means supporting said first contact and tending to force said first contact into a preselected relationship with said second contact, a first bearing element on said supporting means, a second bearing element supported upon said base, a wire connectable in the input circuit and adapted to elongate in response to current therethrough, and two anchor means spaced from both of said bearing elements for fixing the ends of said wire relative to said base, one end of said wire being fixed to one of said anchor means, the other end of said wire being fixed to the other one of said anchor means, said wire engaging said second bearing elementat one point in its length and engaging said first bearing element at two spaced-apart points on its length. I

4. A relay mechanism responsive to current flow in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and second mateable electrical contacts connectable in the output circuit, means securing said second contact on said base, a cantilever spring controlling the position of said first contact and so supported upon said base as to exert a force tending to move said first contact in one direction into a preselected positional relationship with said second contact, a wire connectable in the input circuit and adapted to elongate in response to current therethrough, a first bearing element supported by said spring, two anchor means spaced from one another and spaced substantially equidistantly from said bearing element for anchoring the ends of said wire to the base, a second bearing element remote from said first bearing element and substantially equidistantly spaced from said two anchor means, said wire engaging both of said bearing elements.

5. A relay mechanism responsive to current flow in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and second mateable electrical contacts connectable in the output circuit, means securing said second contact on said base, a cantilever spring controlling the position of said first contact and so supported upon said base as to exert a force tending to move said first contact in one direction into a preselected positional relationship with said second contact, a wire connectable in the input circuit and adapted to elongate in response to current therethrough, a first bearing element supported by said spring, two anchor means spaced from one another and spaced substantially equidistantly from said bearing element for anchoring the ends of said wire to the base, a first bearing element supported by said spring, a second bearing element remote from said first bearing element and substantially equidistantly spaced from said two anchor means, said wire engaging both of said bearing elements, said second bearing element being eccentrically mounted and manually rotatable.

6. A relay mechanism responsive to current fiow in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and second mateable electrical contacts connectable in the output circuit, means securing said second contact on said base, a cantilever spring controlling the position of said first contact and so supported upon said base as to exert a force tending to move said first contact in one direction into a preselected positional relationship with said second contact, a portion of said spring being ofiset, a roller having oppositely extending shaft portions engageable with the offset portion of said spring, and a wire connectable in the input circuit and adapted to elongate in response to current therethrough, a portion of said wire being anchored to said base and another portion passing around said roller, said wire retaining said roller in position on said spring.

7. A relay mechanism responsive to current How in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and second mateable electrical contacts connectable in the output circuit, means securing said second contact on said base, a cantilever spring controlling the position of said first contact and so supported upon said base as to exert a force tending to move said first contact in one wire connectable in the input circuit and adapted to elongate in response to current therethrough, a portion of said wire being anchored to said base and another portion passing around said roller, said Wire retaining said roller in position on said spring and being adapted to exert a force through said roller and upon said spring in a direction opposite to said one direction.

8. A relay mechanism responsive to current flow in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and second mateable electrical contacts connectable in the output circuit, means securing said second contact on said base, a cantilever spring controlling the position of said first contact and so supported upon said base as to exert a force tending to move said first contact in one direction into a preselected positional relationship with said second contact, a portion of said spring being offset and apertured, a roller having oppositely extending shaft portions engageable with the offset portion of said spring, portions of said roller extending through. the aperture in said spring, and a wire connectable in the input circuit and adapted to elongate in response to current therethrough, said wire retaining said roller in position on said spring.

9. A relay mechanism responsive to current flow in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and second mateable electrical contacts connectable in the output circuit, means securing said second contact on said base, a cantilever spring controlling the position of said first contact and so supported upon said vase as to exert a force tending to move said first contact in one direction into a preselected positional relationship with said second contact, a portion of said spring being offset, a roller having oppositely extending shaft portions engageable with the offset portion of said spring, a bearing element spaced from said roller and supported on said base, and a wire connectable in the input circuit and adapted to elongate in response to current therethrough, said wire passing around said roller and around said bearing element and retaining said roller in position on said spring.

10. A relay mechanism responsive to current flow in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and second mateable, electrical contacts connectable in the output circuit, means securing said second contact on said base, a cantilever spring controlling the position of said first contact and so supported upon said base as to exert a force tending to move said first contact in one direction into a preselected positional relationship with said second contact, a portion of said spring being offset and apertured, a roller having oppositely extending shaft portions engageable with the offset portion of said spring, portions of said roller extending through the aperture in said spring, a bearing element spaced from said roller and supported on said base, a wire connectable in the input circuit and adapted to elongate in response to current therethrough, and means anchoring both ends of said wire to said base, said wire passing around said hearing element and twice around said roller, said wire retaining said roller in position on said spring and being adapted to exert a force through said roller on said spring in a direction opposite to said one direction.

11. A relay mechanism responsive to current flow in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and second mateable electrical contacts connectable in the output circuit, means securing said second contact on said base, a cantilever spring controlling the position of said first contact and so supported upon said base as to exert a force tending to move said first contactin one direction into a preselected positional relationship with said second contact, a portion of said spring being otfset and apertured, a roller having oppositely extending shaft portions engageable with the ofiset portion of said spring, portions of said roller extending through the aperture in said spring, a bearing element spaced from said roller and supported on said base, a wire connectable in the input circuit and adapted to elongate in response to current therethrough, and means anchoring both ends of said wire to said base, said wire passing around said bearing element and twice around said roller, said wire retaining said roller in position on said spring and being adapted to exert a force through said roller on said spring in a direction opposite to said one direction, said bearing element being eccentrically mounted on said base and manually rotatable.

12. A relay mechanism responsive to current flow in an input electrical circuit for controlling the current in an output electrical circuit comprising a base, first and sec ond mateable electrical contacts connectable in the output circuit, means securing said second contact on said base, a cantilever spring controlling the position of said first contact and so supported upon said base as to exert a force tending to move said first contact in one direction into a preselected positional relationship with said second contact, a first bearing element supported upon said spring, a wire engaging said first bearing element at a plurality of spaced-apart portions of its length and connectable in the input circuit and adapted to elongate in response to current therethrough, an additional bearing element mounted on said base and spaced from said first bearing element, said wire having a portion engaging said additional bearing element, and a pair of spaced-apart anchor means for anchoring the ends of said wire and positioned to cause said wire to exert plural equal forces in the same direction on said first bearing element, one end of said wire being fixed to one of said anchor means, the other end of said wire being fixed to the other one of said anchor means.

References Cited in the file or this patent UNITED STATES PATENTS 923,839 Henry June 8, 1909 1,804,709 Shoenberg May 12, 1931 1,868,500 Hanel July 26, 1932 2,126,199 Lilja Aug. 9, 1938 2,166,498 Lacey July 18, 1939 2,225,086 Schramm Dec. 17, 1940 2,312,974 Owens Mar. 2, 1943 2,692,955 Lewis Oct. 26, 1954 FOREIGN PATENTS 17,519 Norway June 12, 1907 757,112 France June 17, 1933 828,270 Germany Ian. 17, 1952 

